Abstract
With the aid of immunohistochemistry, the present review attempts to demonstrate the composite fibers and nerve topographical anatomy in the vaginal supportive tissues. Along the tendinous arch of the pelvic fasciae, distal parts of the pelvic plexus extend antero-inferiorly and issue nerves to the internal anal sphincter as well as the cavernous tissues. At the attachment of the levator ani muscle to the rectum, smooth muscles in the endopelvic fascia lining the levator ani merge with the longitudinal smooth muscle layer of the rectum to provide the conjoint longitudinal muscle coat or the longitudinal anal muscle (LAM: smooth muscle). However, at the rectovaginal interface, the longitudinal smooth muscle layer of the rectum continues to the LAM without any contribution of the endopelvic fascia. The bilateral masses of the perineal smooth muscles (PSMs) are connected by the perineal body, and the PSMs receive 1) the longitudinal anal muscle, 2) the internal and external anal sphincters and, 3) the perineal membrane lining the vestibular wall. Tensile stress from the levator ani seems to be transferred to the PSMs via the LAM. Because of their irregularly arrayed muscle fibers, instead of a synchronized contraction in response to nerve impulses, the PSMs are likely to act as a barrier, septum or protector against mechanical stress because, even without innervation, such smooth muscle fibers resist (not absorb) pressure, in accordance with Bayliss’ rule. The external anal sphincter, a strong striated muscle, inserts into the PSMs and seems to play a dynamic role in supporting the rectovaginal interface to maintain the antero-posterior length of the urogenital hiatus. However, we do not think that smooth muscles play an active traction role without cooperation from striated muscle. The fibrous skeleton composed of smooth muscle in the female perineum is explained in terms of a “catamaran” model.
Highlights
The vaginal support structures comprise a series of connective tissues that are well known to gynecologists, i.e., levels I, II and II described by DeLancey [1,2,3]
Tensile stress from the levator ani seems to be transferred to the PSMs via the LAM. Because of their irregularly arrayed muscle fibers, instead of a synchronized contraction in response to nerve impulses, the PSMs are likely to act as a barrier, septum or protector against mechanical stress because, even without innervation, such smooth muscle fibers resist pressure, in accordance with Bayliss’ rule
Muscle contraction force for action and passive mechanical stress can be transferred through a series of collagenous tissues of different types
Summary
The vaginal support structures comprise a series of connective tissues that are well known to gynecologists, i.e., levels I, II and II described by DeLancey [1,2,3]. Soga et al [5] demonstrated a distinct connective tissue mass in the lateral side of the distal vagina, which they termed a difficult name, the lateral extension of the perineal body They considered that the connective tissue, comprising mainly smooth muscles alongside the vestibule, is located adjacent to and connects with both the external and internal anal sphincters, suggesting functional cooperation between the va-. Using histology and macroscopic slices, Stein and DeLancey [7] found that both the compressor urethrae and urethrovaginal sphincter are closely “associated” with the female perineal membrane. In their photos, it was difficult to identify the composite fibers of the membrane. We focused on nerves passing in and along the vaginal supportive tissues, as nerves in the lower paracolpium seem to correspond to the distal part of the pelvic autonomic nerve plexus [10,11,12,13]
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